1. Technical Field of the Invention
The present invention relates generally to a manufacturing method of a gas sensor which may be used in air-fuel ratio control of automotive internal combustion engines and a manufacturing machine therefore, and more particularly to a manufacturing method and machine for such a gas sensor which is capable of establishing a hermetic seal in the gas sensor reliably.
2. Background Art
Japanese Patent Publication No. 2847418 discloses a typical gas sensor used to measure an oxygen content of exhaust gasses of an automotive internal combustion engine. In this sensor, a cup or cover is joined to a sensor holder by staking, therefore, a sufficient degree of sealing between a sensor element and the atmosphere, i.e., the outside of the cover is not obtained.
It is therefore an object of the invention to provide an improved manufacturing system for a gas sensor which is capable of establishing a required hermetic seal in the gas sensor.
According to the first aspect of the invention, there is provided a gas sensor manufacturing method which comprise the steps of: (1) preparing an assembly which has a length and includes (a) a housing which has a length made up of a first end portion, a second end portion, and a flange between the first and second end portions, (b) a cover which is made up of a small-diameter portion, a large-diameter portion, and a shoulder formed between the small-diameter portion and the large-diameter portion, (c) a first insulation porcelain disposed in the large-diameter portion of the cover in contact with the shoulder through an elastic member, (d) a second insulation porcelain disposed in the housing in contact of an end thereof with an end of the first insulation porcelain in alignment with each other, and (e) a laminated sensor element disposed in the second insulation porcelain; (2) pressing the cover against the housing in a lengthwise direction of the assembly to fit an end of the large-diameter portion of the cover on the first end portion of the housing to form an overlap; (3) tacking the large-diameter portion of the cover to the first end portion of the housing at the overlap while pressing the cover against the housing; (4) rotating the assembly about the length thereof; and (5) welding the large-diameter portion of the cover to the first end portion of the housing over the overlap.
In the preferred mode of the invention, the pressing steps presses the cover against the housing while compressing the elastic member to urge the second insulation porcelain against an inner wall of the housing elastically to establish a hermetic seal between an outer wall of the second insulation porcelain and the inner wall of the housing.
The welding step is performed while pressing the cover against the housing.
The pressure exerted on the cover may alternatively be released after the tacking step.
The welding step is performed by laser welding.
The tacking step makes at least two tack welds in the overlap of the cover and the housing.
According to the second aspect of the invention, there is provided a gas sensor manufacturing method which comprises the steps of: (1) preparing an assembly which has a length and includes (a) a housing which has a length made up of a first end portion, a second end portion, and a flange between the first and second end portions, (b) a cover which is made up of a small-diameter portion, a large-diameter portion, and a shoulder formed between the small-diameter portion and the large-diameter portion, and (c) an insulation porcelain disposed in the large-diameter portion of the cover in contact with the shoulder through an elastic member, (d) a cup-shaped sensor element disposed in the housing; (2) pressing the cover against the housing in a lengthwise direction of the assembly to fit an end of the large-diameter portion of the cover on the first end portion of the housing to form an overlap; (3) tacking the large-diameter portion of the cover to the first end portion of the housing at the overlap while pressing the cover against the housing; (4) rotating the assembly about the length thereof; and (5) welding the large-diameter portion of the cover to the first end portion of the housing over the overlap.
In the preferred mode of the invention, the pressing steps presses the cover against the housing while compressing the elastic member to urge the sensor element against an inner wall of the housing elastically to establish a hermetic seal between an outer wall of the sensor element and the inner wall of the housing.
The welding step is performed while pressing the cover against the housing.
The pressure exerted on the cover may alternatively be released after the tacking step.
The welding step is performed by laser welding.
The tacking step makes at least two tack welds in the overlap of the cover and the housing.
According to the third aspect of the invention, there is provided a gas sensor manufacturing method which comprises the steps of: (1) preparing an assembly which has a length and includes (a) a housing which has a length made up of a first end portion, a second end portion, and a flange between the first and second end portions, (b) a cover which is made up of a small-diameter portion, a large-diameter portion, and a shoulder formed between the small-diameter portion and the large-diameter portion, (c) a first insulation porcelain disposed in the large-diameter portion of the cover in contact with the shoulder through an elastic member, (d) a second insulation porcelain disposed in the housing in contact of an end thereof with an end of the first insulation porcelain in alignment with each other, and (e) a laminated sensor element disposed in the second insulation porcelain; (2) pressing the cover against the housing in a lengthwise direction of the assembly to fit an end of the large-diameter portion of the cover on the first end portion of the housing to form an overlap; and (3) welding the large-diameter portion of the cover to the first end portion of the housing at the overlap while pressing the cover against the housing.
In the preferred mode of the invention, the pressing steps presses the cover against the housing while compressing the elastic member to urge the second insulation porcelain against an inner wall of the housing elastically to establish a hermetic seal between an outer wall of the second insulation porcelain and the inner wall of the housing.
The welding step is performed while rotating the cover and the housing.
The welding step may alternatively be performed while fixing the cover and the housing.
The welding step welds the large-diameter portion of the cover to the first end portion of the housing around an overall periphery of the overlap through laser welding.
According to the fourth aspect of the invention, there is provided a gas sensor manufacturing method which comprises the steps of: (1) preparing an assembly which has a length and includes (a) a housing which has a length made up of a first end portion, a second end portion, and a flange between the first and second end portions, (b) a cover which is made up of a small-diameter portion, a large-diameter portion, and a shoulder formed between the small-diameter portion and the large-diameter portion, and (c) an insulation porcelain disposed in the large-diameter portion of the cover in contact with the shoulder through an elastic member, (d) a cup-shaped sensor element disposed in the housing; (2) pressing the cover against the housing in a lengthwise direction of the assembly to fit an end of the large-diameter portion of the cover on the first end portion of the housing to form an overlap; and (3) welding the large-diameter portion of the cover to the first end portion of the housing at the overlap while pressing the cover against the housing.
In the preferred mode of the invention, the welding step is performed while rotating the cover and the housing.
The welding step may alternatively be performed while fixing the cover and the housing.
The welding step welds the large-diameter portion of the cover to the first end portion of the housing around an overall periphery of the overlap through laser welding.
According to the fifth aspect of the invention, there is provided a gas sensor manufacturing method which comprise the steps of: (1) preparing an assembly which has a length and includes (a) a housing which has a length made up of a first end portion, a second end portion, and a flange between the first and second end portions, (b) a cover which is made up of a small-diameter portion, a large-diameter portion, and a shoulder formed between the small-diameter portion and the large-diameter portion, (c) a first insulation porcelain disposed in the large-diameter portion of the cover in contact with the shoulder through an elastic member, (d) a second insulation porcelain disposed in the housing in contact of an end thereof with an end of the first insulation porcelain in alignment with each other, and (e) a laminated sensor element disposed in the second insulation porcelain; (2) pressing the cover against the housing in a lengthwise direction of the assembly until a pressure exerted on the housing reaches a given pressure level to fit an end of the large-diameter portion of the cover on the first end portion of the housing to form an overlap; and (3) welding the large-diameter portion of the cover to the first end portion of the housing at the overlap while pressing the cover against the housing.
In the preferred mode of the invention, the pressing steps presses the cover against the housing while compressing the elastic member to urge the second insulation porcelain against an inner wall of the housing elastically to establish a hermetic seal between an outer wall of the second insulation porcelain and the inner wall of the housing.
The given pressure level is 1.2 times greater than or equal to an elastic pressure produced by the elastic member.
According to the sixth aspect of the invention, there is provided a manufacturing method which comprise the steps of: (1) preparing an assembly which has a length and includes (a) a housing which has a length made up of a first end portion, a second end portion, and a flange between the first and second end portions, (b) a cover which is made up of a small-diameter portion, a large-diameter portion, and a shoulder formed between the small-diameter portion and the large-diameter portion, and (c) an insulation porcelain disposed in the large-diameter portion of the cover in contact with the shoulder through an elastic member, (d) a cup-shaped sensor element disposed in the housing; (2) pressing the cover against the housing in a lengthwise direction of the assembly until a pressure exerted on the housing reaches a given pressure level to fit an end of the large-diameter portion of the cover on the first end portion of the housing to form an overlap; and (3) welding the large-diameter portion of the cover to the first end portion of the housing at the overlap while pressing the cover against the housing.
In the preferred mode of the invention, the pressing steps presses the cover against the housing while compressing the elastic member to urge the sensor element against an inner wall of the housing elastically to establish a hermetic seal between an outer wall of the sensor element and the inner wall of the housing.
The given pressure level is 1.2 times greater than or equal to an elastic pressure produced by the elastic member.
According to the seventh aspect of the invention, there is provided a gas sensor manufacturing machine designed to produce a gas sensor using an assembly which has a length and includes (a) a housing which has a length made up of a first end portion, a second end portion, and a flange between the first and second end portions, (b) a cover which is made up of a small-diameter portion, a large-diameter portion, and a shoulder formed between the small-diameter portion and the large-diameter portion, (c) a first insulation porcelain disposed in the large-diameter portion of the cover in contact with the shoulder through an elastic member, (d) a second insulation porcelain disposed in the housing in contact of an end thereof with an end of the first insulation porcelain in alignment with each other, and (e) a laminated sensor element disposed in the second insulation porcelain. The machine comprises: (1) a first annular press plate fitted on the first end portion of the housing in engagement with the flange; (2) a second annular press plate fitted on the small-diameter portion of the cover in engagement with the shoulder of the cover; and (3) a pressing means for pressing the cover against the housing in a lengthwise direction of the assembly to fit an end of the large-diameter portion of the cover on the first end portion of the housing to form an overlap; (4) a tacking means for tacking the large-diameter portion of the cover to the first end portion of the housing at the overlap while pressing the cover against the housing; (5) a rotating means for rotating the assembly; and (6) a welding means for welding the large-diameter portion of the cover to the first end portion of the housing over the overlap.
In the preferred mode of the invention, the tacking means and the welding means are implemented by a welding machine including welding heads which are rotatable around the overlap.
According to the eighth aspect of the invention, there is provided a gas sensor manufacturing machine designed to produce a as sensor using an assembly which has a length and includes (a) a housing which has a length made up of a first end portion, a second end portion, and a flange between the first and second end portions, (b) a cover which is made up of a small-diameter portion, a large-diameter portion, and a shoulder formed between the small-diameter portion and the large-diameter portion, and (c) an insulation porcelain disposed in the large-diameter portion of the cover in contact with the shoulder through an elastic member, (d) a cup-shaped sensor element disposed in the housing. The machine comprises: (1) a first annular press plate fitted on the first end portion of the housing in engagement with the flange; (2) a second annular press plate fitted on the small-diameter portion of the cover in engagement with the shoulder of the cover; (3) a pressing means for pressing the cover against the housing in a lengthwise direction of the assembly to fit an end of the large-diameter portion of the cover on the first end portion of the housing to form an overlap; (4) a tacking means for tacking the large-diameter portion of the cover to the first end portion of the housing at the overlap while pressing the cover against the housing; (5) a rotating means for rotating the assembly, and (6) a welding means for welding the large-diameter portion of the cover to the first end portion of the housing over the overlap.
In the preferred mode of the invention, the tacking means and the welding means are implemented by a welding machine including welding heads which are rotatable around the overlap.